Identifying treatment protocols by translating required fluoride thresholds into site-specific removal requirements in community-based defluoridation systems

Abstract

Community-scale defluoridation systems have been widely implemented in fluoride-affected, groundwater-dependent regions to mitigate and/or reduce the risks associated with exposure to excessive geogenic fluoride in drinking water [1, 2]. Performance of these systems is typically assessed by whether treated water meets a desired guideline threshold concentration (e.g., 1.5 mg/L fluoride, as prescribed by the World Health Organization) [3]. However, translating that threshold into practice requires a site-specific metric: the fluoride removal efficiency needed to reach the target from local source-water fluoride concentrations. Because this requirement varies across sites (and potentially seasons), treatment protocols should be set against the required removal rather than applying uniformly across all sites. Here, we quantify site-specific required removal targets and compare them with achieved/actual removal using paired pre- and post-treatment measurements. We applied this framework to 58 community water purification plants (CWPPs) in the Bankura and Purulia districts of West Bengal, India, to quantify required versus achieved removal across sites and identify where operational intensity (e.g., media choice, run time, regeneration frequency) should differ.

Pre-filter fluoride ranged from 1.6 to 8.2 mg/L. To meet the WHO guideline of 1.5 mg/L, required removal efficiencies were 11.8 to 81.7 % in Bankura (median 54.5 %) and 6.3 to 61.5 % in Purulia (median 28.6 %), with an overall median requirement of 33.3 % across both districts. Even for a stricter target of 1.0 mg/L, median required removal largely remained below 70 %. Together, these results show that many community systems do not need near-complete fluoride removal; they require a clearly defined, site-specific removal target that can range from moderate to very high. This spread is operationally consequential; a plant requiring ~30 % removal should not be managed with the same media choice, run time, or regeneration frequency as one requiring ~80 % removal.

Based on the required fluoride removal (derived from source-water fluoride and the selected threshold concentrations) and ideally tracked across seasons, this approach can tailor site-specific operation of the community defluoridation system, guiding adsorbent media choice for different sites, run times, monitoring and regeneration frequency, and maintenance scheduling. In doing so, it will help operators set realistic performance targets, detect underperformance early, and prioritize corrective actions where needed the most.

References

1. Khairnar et al. (2015). doi:10.7860/JCDR/2015/13261.6085

2. Osterwalder et al. (2014). doi:10.1016/j.scitotenv.2013.10.072

3. WHO (2022). Guidelines for drinking-water quality

Acknowledgements

This work was supported by the Australia-India Institute (Grant: 053139) and the Manchester-Melbourne PhD funding (Cookson Scholars) to AK. Additional support included contribution from The University of Manchester, UKRI (MR/Y016327/1) to LAR et al. We thank colleagues at the University of Manchester, IIT Kanpur, IIT Kharagpur, WBPHED staff, and communities in West Bengal for support with the project and field sampling. The views expressed are those of the authors.